Wear-resistant, superabrasive compacts are utilized for a variety of mechanical applications. For example, polycrystalline diamond compacts (“PDCs”) are used in drilling tools (e.g., cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and in other mechanical systems.
PDCs have found particular utility as superabrasive cutting elements in rotary drill bits, such as roller cone drill bits and fixed cutter drill bits. A PDC cutting element or cutter typically includes a superabrasive diamond layer or table. The diamond table is formed and bonded to a substrate using a high pressure, high temperature (“HPHT”) process. The substrate is often brazed or otherwise joined to an attachment member such as a stud or a cylindrical backing. A stud carrying the PDC may be used as a PDC cutting element when mounted to a bit body of a rotary drill bit by press-fitting, brazing, or otherwise securing the stud into a receptacle formed in the bit body. The PDC cutting element may also be brazed directly into a preformed pocket, socket, or other receptacle formed in the bit body. Generally, a rotary drill bit may include a number of PDC cutting elements affixed to the drill bit body.
Conventional PDCs are normally fabricated by placing a cemented carbide substrate into a container or cartridge with a volume of diamond particles positioned on a surface of the cemented carbide substrate. A number of such cartridges may be typically loaded into an HPHT press. The substrates and volume of diamond particles are then processed under HPHT conditions in the presence of a metal-solvent catalyst that causes the diamond particles to bond to one another to form a matrix of bonded diamond grains defining a diamond table. The metal-solvent catalyst is often a solvent catalyst, such as cobalt, nickel, or iron that is used for facilitating the intergrowth of the diamond particles.
In one conventional approach, a constituent of the cemented carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt acts as a catalyst to facilitate intergrowth between the diamond particles, which results in formation of bonded diamond grains.
The presence of the solvent catalyst in the diamond table is believed to reduce the thermal stability of the diamond table at elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the solvent catalyst is believed to lead to chipping or cracking in the PDC during drilling or cutting operations, which consequently can degrade the mechanical properties of the PDC or cause failure. Additionally, some of the diamond grains can undergo a chemical breakdown or back-conversion with the solvent catalyst. At extremely high temperatures, portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thus, degrading the mechanical properties of the PDC.
Therefore, manufacturers and users of polycrystalline diamond materials continue to seek improved thermally stable, polycrystalline diamond materials and processing techniques.